The present application relates to an ink fountain mechanism for a rotary offset printing press, and in particular to an ink liner control mechanism.
An ink fountain, or ink duct as it is sometimes called, is commonly connected on a rotary offset printing press for supplying ink to a fountain roller, or ductor roller. The fountain roller rotates through the ink in the ink fountain reservoir. The ink is received onto the surface of the fountain roller and then is rollingly transferred, directly or through a series of intermediate rollers, to a printing roller. It is desirable to adjust the quantity of ink received by the fountain roller so that an adequate supply of ink is provided to the printing roller while minimizing excess ink. The amount of ink required will depend upon various factors such as the viscosity of the ink, the type of paper and importantly, the density of the printing or image. The adjustment of the quantity of ink is accomplished by adjusting the thickness of the film, or the layer, of ink that the fountain roller receives onto its surface. The ink is then transferred from the ink fountain to a printing roller and then onto the printed sheet.
The density of the printing also typically varies across the printed sheet. Particularly, in the case of multiple color printing, the amount of any given color of ink may vary across the sheet, depending upon the density of the particular color in the printed image. Therefore, it is further desirable to adjust and vary the quantity of ink supplied by the fountain roller to different areas according to the print density of the different colors. To better approximate the amount of ink needed in different areas of a given sheet of printing, a plurality of axially spaced zones are identified along the length of the fountain roller. The adjustment of the quantity of ink is accomplished by adjusting the thickness of the film or layer of ink that the fountain roller receives onto its surface in each of the zones. The ink is then transferred more completely from the ink fountain to a printing roller and then onto the printed sheet with minimal waste and with improved print quality.
In the past the adjustment of the quantity of ink was attempted using an ink blade at the bottom of the ink reservoir supported at an angle against the fountain roller. The edge of the ink blade was spaced from the fountain roller a small distance forming a gap through which the ink was squeezed into a layer or film as the roller rotated. A thin ink blade was supported along its dispensing edge by the rounded tips of adjustable bolts. The bolts could be threaded in and out to adjust the pressure on the blade in the area of the bolt tips for approximated zonal control. It was found that because of the point pressure of the tips of the bolts, this mechanism for metering the quantity of ink in different zones needed improvement.
The present invention provides a unique, simplified, reliable and improved ink fountain mechanism for adjustably metering the thickness of the layer of ink in a plurality of zones axially across a fountain roller. The ink fountain mechanism includes a plurality of metering blocks, horizontally aligned and axially adjacent to one another and each having an upper surface adjustably spaced from an ink receiving fountain roller. A plurality of adjustment bolts are each separately and threadably engaged with each of the plurality of metering blocks. The adjustment bolts are slideably supported in a main beam that extends the length of the fountain roller. A plurality of lever actuated cams are pivotably held adjacent to the heads of each of the adjustment bolts. The cams are engaged with the heads of the adjustment bolts and are actuatable between a minimum position, providing a minimum metered ink thickness, and a maximum position, providing maximum metered ink thickness. The lever actuating the cam is continuously movable between the minimum and maximum positions to provide substantially continuous metering of the thickness of ink in a range between the minimum and the maximum ink thicknesses.
According to one embodiment the adjustment bolts are biased toward the cam. For example, a return spring may be held in the main beam so that it pushes against a bottom of the adjustment bolt head and such that the top of the adjustment bolt head is biased to interface against the cam. In an exemplary embodiment, the bolt head interfaces against the cam through a interface cap constructed of a material selected to provide non-binding frictional sliding contact between the cam and the cap. The size, shape and materials of the interface between the cap and the cam are selected and constructed so that the cam lever can be manually moved through the range of ink thickness metering positions, yet the cam lever and cam will remain in any desired metering position by the frictional contact between the cam and the cap. External force applied to the cam lever is required to change the metering position. In an exemplary embodiment the lever is moveable by a press operator with manually applied force. Each of the cam levers may be separately positioned to meter the ink thickness at each of the separate metering blocks.
According to another aspect the invention each cam is mounted on a mounting shaft for rotation between the minimum and maximum metering positions. Orifices are formed through the cam and the mounting shaft, that may be aligned to permit an adjustment tool to be extended through the cam and through the mounting shaft. The adjustment tool engages with the head of the adjustment bolt to thread the bolt into or out of the metering block and to thereby precisely position the metering block relative to the main beam and to the fountain roller. The threaded bolt adjustment is thus useful for precisely adjusting the minimum thickness of the ink when the cam is at its minimum position. The maximum thickness of the ink will also be adjusted upon adjusting the minimum thickness because the eccentric lift of the cam between the minimum position and the maximum position remains constant. For example, if the eccentric lift of the cam is thirty thousandths of an inch, from the minimum to the maximum positions, and the minimum ink thickness is adjusted from one thousandth of an inch thick down to zero, the maximum thickness will be adjusted from thirty-one thousandths of an inch thick to thirty thousandths of an inch thick.